In order not to provoke any irritations for an observer of a dynamically variable image, an image refresh frequency should be sufficiently high or an image set-up time should be sufficiently short. For stationary image surfaces, e.g. screens for television pictures or videos, an image refresh frequency of at least 25 Hz is required. However, if light is projected into a far field at a distance of at least two meters, and if, in addition, the light emission pattern varies dynamically, a much higher image refresh frequency may be necessary in order to avoid irritations for an observer on account of image transitions not being perceived as fluid. In addition, in the case of projections into the far field, a much higher light power is typically required in order to achieve a sufficiently bright illumination. Therefore, in many cases, the dynamic light emission pattern in the far field cannot be generated or can be generated only in a very complex fashion by means of a single light source with sufficient dynamic range, e.g. cannot be generated by a single semiconductor light source such as an LED or a laser diode.
One possibility for providing an increased dynamic range consists in the use of a conventional light source having a high light power, e.g. a halogen lamp, downstream of which is disposed an optical unit moved by motor. However, this is very complex and not very robust and restricts a shaping of a light emission pattern to a small number of fixedly predefined shapes. So-called “leveling motors” are often used for the movement of the optical unit by motor.
A further possibility for providing an increased dynamic range consists in the use of an array of many LEDS (“LED array”), wherein respective subgroups of the LEDs are switched on depending on the desired light emission pattern. What is disadvantageous here is that a large number of LEDs must be kept available, only a minority of which are used in practice for a specific emission pattern. The degree of utilization is therefore low, which entails high costs, inter alia.
Moreover, a plurality of disjoint (non-overlapping) partial regions of a phosphor surface may be illuminated independently of one another by respective spaced-apart light generating units. What is disadvantageous in this case is that a high number of light generating units must be used. In practice, these light generating units are operated in a dimmed fashion most of the time, unless small, locally delimited, bright regions are intended to be generated in the light emission pattern. Consequently, a degree of utilization is low in this case, too. Moreover, spatially and temporally coordinating the respectively generated partial light emission patterns in order to generate a uniformly perceived total light emission pattern is difficult.
WO 2011/160680 A1 discloses a light source arrangement including a primary light source and a secondary light source, wherein the primary light source is designed to illuminate the secondary light source, wherein the secondary light source comprises a polyhedron having at least one first and one second phosphor surface, wherein the primary light source includes at least one laser or one light emitting diode, and wherein a drive mechanism is fixed to the primary light source or to the secondary light source.
US 2006/0227087 A1 discloses laser display systems which generate at least one scanning laser beam in order to excite one or more fluorescent materials on a screen which emits light in order to form images. The fluorescent materials may include phosphor materials.
EP 2 359 605 B1 discloses an illuminant including at least one semiconductor laser which is designed to emit a primary radiation having a wavelength of between 360 nm and 485 nm inclusive, and at least one conversion means which is disposed downstream of the semiconductor laser and is designed to convert at least part of the primary radiation into a secondary radiation having a longer wavelength different than the primary radiation, wherein the radiation emitted by the illuminant has an optical coherence length amounting to at most 50 micrometers, wherein the conversion means has a concentration of color centers or luminous points which amounts to at least 10^7/μm^3 and the color centers or luminous points are distributed statistically in the conversion means, and wherein a focal spot of the conversion means that is irradiated by the primary radiation has an area of at most 0.5 mm^2.